Seeds in buds,is this normal?

Hi All.I'm posting this for a friend who's is nearly ready to harvest his crop of Big Buddha Cheese but phoned me to say that about five of his twenty plants contained many seeds in the buds.There's no male plants anywhere,they were all grown from feminised seeds and they've had absolutely no stress whatsoever.He says they're absolutely covered in big dense buds but was just worried about the amount of seeds a few of them contained.Can anyone tell me if this is normal sometimes or does he have some sort of problem?

Either got pollen brought in on himself, through a window/vent, or had a couple hermie flowers. Can't get seed without pollen.